A dual turbine power plant includes first and second turbine-generators connected to use steam from a common source. In a single turbine plant the steam source supplies one turbine-generator. A malfunction of the turbine-generator or its associated steam supply piping and steam condenser in such a single turbine plant may require shutting down the entire generating capacity until necessary repairs are made. In a dual turbine plant, however, such a malfunction may require shutting down one, but not both, of the turbine-generators, in which event one-half the generating capacity continues to operate while repairs are made.
In event that the steam source includes a high temperature gas cooled nuclear reactor, reactor-generated heat is delivered to a steam generator by a coolant gas that is circulated through the reactor and the steam generator. The steam generator is connected to supply super-heat and reheat steam to the dual turbine-generators. Each turbine comprises a high pressure portion driven by super-heat steam and a lower pressure portion driven by reheat steam. To protect the steam generator from low steam flow, a bypass line is connected across each of the turbine portions to permit at least a minimum flow of steam from the source when the turbine flow is less than the minimum. A gas circulator propels the coolant gas through the reactor and the steam generator; such a circulator advantageously may be driven by an auxiliary steam turbine which uses steam from the steam source. Typically such a turbine is connected to use steam emanating from the high pressure turbine portions and their bypass lines, before such steam is reheated.
In a power plant having turbines that use reheat steam it is desirable to control the pressure of such steam as it is discharged from the steam source, as a controlled pressure of that steam results in improved control of the speed or of the power output of the turbine portions which are driven by the reheat steam. If such a power plant includes a high temperature gas cooled reactor in its steam supply and auxiliary steam turbines as above described, such a controlled pressure further benefits control of the differential pressure across the auxiliary turbines, and thus improves control of the rotational speed of those turbines and of the flows of the coolant gas through the reactor.
In a proposed system for controlling the pressure of reheat steam in a power plant having a single turbine generator and a high temperature gas cooled nuclear reactor in its steam supply, a controller including both proportional and integral control modes governs the flow of reheat steam through a bypass line. However, application of two such controllers to operate in concert in a dual turbine plant may cause unwanted imbalance of the steam flows through the bypass lines which conduct reheat steam, as a result of the integral control modes.
In a proposed system for controlling the pressure of reheat steam in a dual turbine power plant which incorporates a high temperature gas cooled reactor in its steam supply, such pressure is controlled by dual proportional-only controllers, each of which governs the flow through a respective bypass line for conducting reheat steam, in order to regulate the pressure of the reheat steam. A limitation of the system is that it permits a non-zero steady state difference between the controlled pressure and its desired value. Another limitation is that an imbalance between the proportional gains of the two controllers may cause an imbalance between the flows through the bypass lines at times when the flows otherwise desirably would be balanced.
There appears to be a need for a system for controlling the pressure of reheated steam in a power plant that includes dual turbine-generators connected to a common steam source. Such a system desirably reduces a difference between a detected value of such pressure and a desired value of the pressure to a zero steady state level. A desirable feature of a power plant that includes the system is that there are no unwanted imbalances between the flows through the bypass lines that conduct reheated steam, which imbalances otherwise may result from changes of control gains that are used for regulating the flows through the bypass lines. An additional advantage of a power plant that includes the system is that reheated steam may be bypassed to an alternate steam receiving means to prevent a bypass flow of such steam to a condenser from exceeding a limit value which varies with a detected characteristic of the reheated steam. Thus an excessive heat dump rate to the condenser is prevented.
The description of prior art herein is made on good faith and no representation is made that any prior art considered is the best pertaining prior art nor that the interpretation placed on it is unrebuttable.